1. Field of the Invention
The present invention relates to a molded motor.
2. Description of the Related Art
A molded motor including a resin casing opened at one axial end and a stator covered with a resin and embedded in the casing is known (see, e.g., Japanese Patent Application Publication No. 2002-335649). The stator of the molded motor includes a metal stator core. Stator coils are wound on respective tooth portions of the stator core. A rotor including a shaft is arranged radially inward of the stator. The shaft is rotatably supported by a pair of bearings.
A cylindrical bearing housing is molded as a single piece with the casing in the bottom wall portion of the casing. One of the bearings is fitted into the bearing housing. The open side of the casing is covered with a metal bracket cover. The bracket cover includes a cylindrical bearing housing. The other bearing is fitted to the cylindrical bearing housing of the bracket cover.
As disclosed in Japanese Patent Application Publication No. 2002-335649, the bracket cover is made of a metallic material which has an increased rigidity and superior workability. Thus, the bearing is assembled with the bracket cover such that it possesses increased accuracy. This helps reduce the shaft from being off-centered and assists in enhancing the rotational accuracy of the rotor.
In this case, the metal bracket cover and the metal stator core are arranged with a resin interposed there between as a dielectric body. For that reason, if a motor is PWM-controlled, an electric potential difference is generated between the bracket cover and the stator core and an electric current circulates along a route defined by the stator core, the stator coils, the bearing, the shaft, the rotor and the stator core. As s consequence, it is sometimes the case that the bearings are damaged due to electric corrosion.